void main() {
  // 1. 声明变量
  var name = '张三', age = 18;

  // 2. 修改变量
  name = '李四';
  age = 30;

  // 3. var声明的变量支持类型推断
  // A value of type 'int' can't be assigned to a variable of type 'String'.
  // name = 100;

  print({name, age});
}
